Control of various pests through the use of biological molecules has been possible in only a limited number of cases. The best known examples of biological molecules with pesticidal uses are the .delta.-endotoxins from Bacillus thuringiensis (Bt). Various strains of Bt are known which produce insecticidal proteins, the .delta.-endotoxins, during sporulation. Some of these .delta.-endotoxins have useful insecticidal activities against different insect pests. However, use of the .delta.-endotoxins is limited because they are active against only a very few of the many insect pests.
The limited specificity of the Bt endotoxins is dependent, at least in part, on both the activation of the toxin in the insect gut (Haider, M. Z. et al., 1986, Eur. J. Biochem. 156:531-540) and its ability to bind to specific receptors present on the insect's midgut epithelial cells (Hofmann, C. P. et al., 1988, PNAS 85:7844-7848). Among the factors which prevent activity of a particular Bt .delta.-endotoxin against a specific insect is the lack of appropriate receptors in the insect gut or lack of affinity of the .delta.-endotoxin for the receptors which may be present, thus resulting in no binding of the .delta.-endotoxin to the brush border membranes. Therefore, the ability to control a specific insect pest using Bt .delta.-endotoxins at present depends on the ability to find an appropriate .delta.-endotoxin with the desired range of activity. In many cases, no such .delta.-endotoxin is known, and it is not certain that one even exists. For example, thousands of Bt strains have been screened for activity against western corn rootworm (WCRW), a major pest of maize. However, to date there are no reports of strains of Bt which produce a .delta.-endotoxin that is highly effective against WCRW.
Individual .delta.-endotoxins typically have a very narrow spectrum of activity, each being active against only one or a few insect pests. Moreover, the .delta.-endotoxins have been shown to be active against only a few members of but a small number of Orders of insects. The ability to produce additional proteins with unique pesticidal activities creates more options for the control of agricultural pests, particularly insects, using biological molecules with a high level of safety for non-target organisms. Thus, there is a need for binding proteins which can be designed to target a particular insect pest.